Abstract Soil gas and Electrical Resistivity Tomography (ERT) surveys were performed in Medolla (Emilia-Romagna Region, northern Italy) within a farming area characterized by macroseeps, absence of vegetation and anomalous temperatures of soil to investigate the soil gas migration mechanism and verify the presence of a buried fault intersecting the macroseeps. Soil gas (222Rn, 220Rn, He and C2H6) concentrations and flux (φCO2 and φCH4) measurements were carried out from 2008 to 2015, comprising the 2012 Emilia seismic sequence. Moreover, in 2016 a ERT survey, combined with new flux measurements, was performed along four profiles (ranging from 180 to 630 m long) centered on the main macroseep. We found that the seismic sequence sensibly influenced the soil gas distribution in the area. All investigated species, but He, increased their values early after the mainshocks, likely due to crustal deformation which promoted the geogas uprising. In 2015, when the stress has vanished, these concentrations gradually decreased toward pre-seismic values. Helium concentrations showed an opposite behavior as they decreased in May 2012 and then gradually increased over time. This trend may be reasonably due to the enhancement of the strain field which promoted the He dissipation from soil to the atmosphere, due to its high volatility. In all the geochemical surveys conducted from 2008 to 2015, soil gas high values around the main macroseeps were identified, delighting the presence of an alignment in the E-W direction. This trend, identified for several gas species, ultimately supports the theory of a hidden fault which favors the intensification of fluids migration along zones characterized by greater permeability. ERT results highlighted a sub-horizontal layering characterized by different resistivity intervals, roughly matching local stratigraphy. In most profiles we observed a slightly increase of resistivity and a sharp interruption of the electro-layering in correspondence of the main macroseep, both near the surface and at depth. This implies that a fracture zone due to the presence of a buried fault cannot be excluded. The combined use of geochemical and geophysical techniques in this study confirmed the usefulness of such multiparametric approach for mapping out hidden structures in tectonically active areas, allowing to better understanding the fluid migration processes through preferential leakage pathways.

中文翻译：

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Terre Calde di Medolla（意大利北部艾米利亚-罗马涅）的地球化学和地电特征以及与 2012 年地震序列的关系

摘要 在 Medolla（意大利北部艾米利亚-罗马涅大区）一个以大渗漏、无植被和土壤温度异常为特征的农业区进行了土壤气体和电阻率断层扫描 (ERT) 调查，以研究土壤气体迁移机制并验证存在与宏观渗漏相交的埋藏断层。土壤气体（222Rn、220Rn、He 和 C2H6）浓度和通量（φCO2 和 φCH4）测量是从 2008 年到 2015 年进行的，包括 2012 年艾米利亚地震序列。此外，在 2016 年，沿着以主要宏观渗漏为中心的四个剖面（长度从 180 到 630 m）进行了 ERT 调查，并结合了新的通量测量。我们发现地震序列显着影响了该地区的土壤气体分布。所有被调查的物种，但他，在主震后的早期，它们的值增加了，这可能是由于地壳变形促进了地气上升。2015 年，当应力消失后，这些浓度逐渐降低至震前值。氦浓度显示出相反的行为，因为它们在 2012 年 5 月下降，然后随着时间的推移逐渐增加。这种趋势可能是由于应变场的增强，促进了 He 从土壤向大气耗散，因为它的高挥发性。在 2008 年至 2015 年进行的所有地球化学调查中，确定了主要宏观渗漏周围的土壤气体高值，令人高兴的是在 EW 方向存在对齐。这种趋势，已确定为几种气体种类，最终支持隐藏断层的理论，该理论有利于流体沿着具有更大渗透性的区域的迁移加剧。ERT 结果突出显示了以不同电阻率区间为特征的亚水平层状结构，大致与当地地层相匹配。在大多数剖面中，我们观察到电阻率略有增加，并且与主要宏观渗漏相对应的电分层急剧中断，无论是在表面附近还是在深处。这意味着不能排除由于埋藏断层的存在而形成的断裂带。本研究中地球化学和地球物理技术的结合使用证实了这种多参数方法在绘制构造活动区的隐藏结构方面的有用性，